Changes

  | part    = Critical elements of the petroleum system

  | part    = Critical elements of the petroleum system

  | chapter = Migration of petroleum

  | chapter = Migration of petroleum

  | frompg  = 7-1

  | frompg  = 7-9

  | topg    = 7-38

  | topg    = 7-11

  | author  = Martin D. Matthews

  | author  = Martin D. Matthews

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch07/ch07.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch07/ch07.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

The ease with which hydrocarbons move through the stratigraphic section is controlled by the petrophysical properties of the [[Pore system fundamentals|pore system]], the mineralogy of the rock, and the properties of the hydrocarbons. These factors determine the preferential pathway of migration from high to low potential energy and are responsible for concentrating or dispersing the hydrocarbons.

The ease with which hydrocarbons move through the stratigraphic section is controlled by the petrophysical properties of the [[Pore system fundamentals|pore system]], the mineralogy of the rock, and the properties of the hydrocarbons. These factors determine the preferential pathway of [[Hydrocarbon migration|migration]] from high to low potential energy and are responsible for concentrating or dispersing the hydrocarbons.

==Pore throats as sieves==

==Pore throats as sieves==

Pore throats act as molecular sieves, allowing particles smaller than the orifice to pass and retaining larger particles. If seals were uniformly composed of the same pore throats, they would be perfect seals for compounds larger than the pore throat apertures.

Pore throats act as molecular sieves, allowing particles smaller than the orifice to pass and retaining larger particles. If seals were uniformly composed of the same pore throats, they would be perfect seals for compounds larger than the [[Pore and pore throat sizes|pore throat apertures]].

[[file:migration-of-petroleum_fig7-3.png|thumb|{{figure number|1}}]]

 

[[file:migration-of-petroleum_fig7-3.png|300px|thumb|{{figure number|1}}Comparison of shale pore size with hydrocarbon molecule size. From Momper;<ref name=Momper1978>Momper, J. A., 1978, [http://archives.datapages.com/data/specpubs/geochem1/data/a034b/a034/0001/0000/t1.htm Oil migration limitations suggested by geological and geochemical considerations], in W. H. Roberts and R. J. Cordel, eds., Physical and Chemical Constraints on Petroleum Migration: AAPG Continuing Education Course Notes Series no. 8, p. B1–B60.</ref> courtesy AAPG.]]

Shale pore sizes range over five orders of magnitude and are about the diameter of the individual hydrocarbon molecules. This suggests many pore throats will be able to pass only the smaller hydrocarbon molecules due to physical restrictions (styric effects). Thus, the larger shale pores are supplied with full-spectrum hydrocarbons migrating directly from [[kerogen]] in contact with the pores. Larger shale pores are also preferentially supplied with the smaller paraffin and aromatics from the neighboring smaller pores. [[:file:migration-of-petroleum_fig7-3.png|Figure 1]] compares shale pore size with hydrocarbon molecule size.

Shale pore sizes range over five orders of magnitude and are about the diameter of the individual hydrocarbon molecules. This suggests many pore throats will be able to pass only the smaller hydrocarbon molecules due to physical restrictions (styric effects). Thus, the larger shale pores are supplied with full-spectrum hydrocarbons migrating directly from kerogen in contact with the pores. Larger shale pores are also preferentially supplied with the smaller paraffin and aromatics from the neighboring smaller pores. [[:file:migration-of-petroleum_fig7-3.png|Figure 1]] compares shale pore size with hydrocarbon molecule size.

==Trapping large molecules in shale==

==Trapping large molecules in shale==

==Permeability==

==Permeability==

[[Permeability]] is related to pore throat size, distribution, and interconnectedness. It is a measurement of the rate at which fluids move through a pore system. The properties of the fluids present in the pores also control the rate at which they move through the system. [[Permeability]] is inversely related to the viscosity of the fluid moving through the pores. The presence of more than one immiscible phase in the pore system reduces the [[permeability]] of each phase below what it would be if it were the only phase present. Permeability measurements are dominantly taken in sands for reservoir engineering purposes and rarely in shales because of difficulties in getting good measurements. Also, permeabilities derived from cores are characteristically lower than those measured during production tests.

[[Permeability]] is related to pore throat size, distribution, and interconnectedness. It is a measurement of the rate at which fluids move through a pore system. The properties of the fluids present in the pores also control the rate at which they move through the system. [[Permeability]] is inversely related to the [[viscosity]] of the fluid moving through the pores. The presence of more than one immiscible phase in the pore system reduces the [[permeability]] of each phase below what it would be if it were the only phase present. Permeability measurements are dominantly taken in sands for reservoir engineering purposes and rarely in shales because of difficulties in getting good measurements. Also, permeabilities derived from cores are characteristically lower than those measured during production tests.

==Capillary forces==

==Capillary forces==

Once a separate phase is formed, capillary forces become effective. Capillary forces arise at the interface between two phases across a restricted opening. [[Capillary pressure]] is a function of the interfacial tension between the immiscible fluids and the pore throat size. As the pressure difference across a capillary restriction increases, the interface deforms and eventually the nonwetting phase penetrates the restriction. Capillary effects only arise at the contact of two immiscible phases. Neither solution transport nor continuous phase is affected by capillary effects. The phase that preferentially wets the grain surfaces (usually water) is continuous. The nonwetting phase is generally assumed to form one or more continuous networks through a bed when its concentration exceeds between 4.5% and 17% of the pore volume.

Once a separate phase is formed, capillary forces become effective. Capillary forces arise at the interface between two phases across a restricted opening. [[Capillary pressure]] is a function of the interfacial tension between the immiscible fluids and the pore throat size. As the pressure difference across a capillary restriction increases, the interface deforms and eventually the nonwetting phase penetrates the restriction. Capillary effects only arise at the [[Fluid contacts|contact of two immiscible phases]]. Neither solution transport nor continuous phase is affected by capillary effects. The phase that preferentially wets the grain surfaces (usually water) is continuous. The nonwetting phase is generally assumed to form one or more continuous networks through a bed when its concentration exceeds between 4.5% and 17% of the pore volume.

==Capillary forces between small pores==

==Capillary forces between small pores==

==Pore pressure==

==Pore pressure==

Differences in pore fluid overpressure determine the potential, general direction, and rate of fluid flow. For hydrocarbons, the force of buoyancy must be added. The spatial distribution of pressure differentials interacts with permeability and capillarity to determine the flow rates along multiple migration pathways. Perfect seals—ones that don't leak at all—rarely occur. Pressure minimums are a perfect seal. When all the forces acting on a hydrocarbon mass are resolved and a local minimum in gradient field occurs, the hydrocarbons will remain in the minimum as long as it exists. There is no migration out of that minimum.

Differences in pore fluid overpressure determine the potential, general direction, and rate of fluid flow. For hydrocarbons, the force of buoyancy must be added. The spatial distribution of pressure differentials interacts with permeability and capillarity to determine the flow rates along multiple [[Hydrocarbon migration|migration]] pathways. Perfect seals—ones that don't leak at all—rarely occur. Pressure minimums are a perfect seal. When all the forces acting on a hydrocarbon mass are resolved and a local minimum in gradient field occurs, the hydrocarbons will remain in the minimum as long as it exists. There is no migration out of that minimum.

==Phase changes==

==Phase changes==

* [[Migration]]

* [[Migration]]

* [[Factors that cause migration]]

* [[Factors that cause migration]]

==External links==

==External links==

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Migration of petroleum]]

[[Category:Migration of petroleum]]